CCD image sensors typically include an array of photosensitive areas (or “pixels”) that collect charge carriers in response to illumination. The collected charge is subsequently transferred from the array of pixels and converted to a voltage from which an image may be reconstructed by associated circuitry. FIG. 1 depicts a conventional interline CCD image sensor 100 that contains an array of photodiodes 110 arranged in columns. A vertical CCD (VCCD) 120 is disposed next to each column of photodiodes 110, and the VCCDs 120 are connected to a horizontal CCD (HCCD) 130. Each photodiode 110 along with its corresponding VCCD 120 constitutes a pixel of the image sensor 100. Following an exposure period, charge is transferred from the photodiodes 110 into the VCCDs 120, which subsequently shift the charge, row-by-row in parallel, into the HCCD. The HCCD then transfers the charge serially to output circuitry 140 that includes, e.g., a floating diffusion sense node and an output buffer amplifier. The charge from the HCCD is converted, pixel-by-pixel, into voltage at the output circuitry 140, and the signal is then transferred to additional circuitry (either on-chip or off-chip) for reconstruction into an image.
Over time, CCD image sensors have grown larger (i.e., incorporated more pixels) and have been utilized in a host of applications, some of which demand high frame rates, e.g., machine vision applications and video display. While innovative CCD image sensor designs incorporating, e.g., multiple output circuits, have enabled higher frame rate, such techniques often cannot provide sufficient performance increases as sensor sizes continue to grow. Furthermore, many CCD image sensors lack the flexibility to operate in multiple modes that trade off resolution for exposure speed. Finally, many CCD imaging methods equipped to capture multiple images in quick succession utilize strobe light sources, as described in U.S. Pat. No. 7,508,436, the entire disclosure of which is incorporated by reference herein, and such light sources are often not suitable for all imaging conditions. Thus, there continues to be a need for CCD-based imaging methods, utilizing a single CCD image sensor, that have the flexibility to provide high-speed imaging modes enabling multiple-image capture without the need for strobe light sources, as well as modes that trade off such speed enhancements for increased resolution.